Motor controller



Nov. 27, 1928.

R. G. THOMPSON MoTon CONTROLLER Filed Nov. y2, 1925 llnwmmm Patented Nev. 27, 1928.

4UNITED STATES PATENT oFFlcE.

RUSSELL G. THOMPSON, OF ROCHESTER, NEW YORK, ASSIGNOR TO NORTH EAST IliLEC-` TRIC COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK..V

MOTOR CONTROLLER.

Application led November 2, 1925. Serial No, 66,425.

This invention relates to a motor controller in the form of arheostat, which is adapted,

in certain details of its construction, particularly for the purpose of controlling the speed of an electric motor, of the so-called universal type although it is also applicable to other uses. f

One object of the invention is to produce a controller particularly adapted for varying the speed of an electric motor by introducing more or less resistance into the circuit of the field winding of the motor, and to this end the invention resides in a rheostat having certain adjustable stops, for limiting its range of movement in accordance with the peculiarities of the motor and with the characteristics of the current by which the motor is energized. Another object of the invention is to produce a rheostat of simple, compact and inexpensive construction, and capable of rapid and wide adjustment in a convenient manner.

Other objects of the invention, and the features of construction by which the several objects are attained, will be set forth more particularly hereinafter.

ln the accompanying drawings, Fig.. 1 is a front-elevation of a motor controller embodying the present invention, with a diagrammatic representation of a motor with which itis associated and oi' a machine, such as a typewriter, in which the motor and the controller are mounted.` In this figure a portion of the controller is broken away to show its construction. Fig. 2 is a bottom-view ofthe controller, shown partly in section on a median horizontal plane; and Fig. 3 is a vertical section on the line 3--3 in Fig. 2.

The controller illustrated in the drawings comprises two resistance devices 5, of generally cylindrical form, mounted on two parallel central rods 6. These rods are fixed! inv the ends of a sheet-metal housing 7 which encloses the resistance devices and is provided ywith a removable front cover 8 place by screws 9.

y secured in Each resistance device comprises a central core of insulating material, as shown in Fig. 3, upon which resistance wire 10 is wound in a helix, the wire; being covered, for the most part, by an 'outer shell or coating 11 of linsulating material. This outer material is removed along a longitudinal band at the front of each resistancedevice expose the wire, so that the turns of wire may serve as the a series of contact-points for engagement with a movable contact-member.

The movable contact member of the rheostat is in the form of a bar 12, of copper or other conductive material, which bears at its ends against thcexposed resistance wires. This bar is moved by va screw 13, of quick pitch-which lies parallel with and between the resistance devices, being journalled, near its ends, in the ends of the housing 7. threaded sleeve or nut 14, of vulcanized fibre or other suitable insulating material, travels upon the screw `and is provided with a forwardly projecting arm 15. The arm passes loosely through an opening in the contact member 12, and' the arm and the opening are made of rectangular form, so that the contact member is in a'position substantially at right-angles with the screw. In order to maintain the ends of the contact-member yieldingly in engagement with the resistance wire,'a helical spring 16 is wrapped around contact-member.

The construction just described permits the contact member to accommodate itself to any slight irregularities in thefform of theresistance devices, while it is moved transversely by the action of the screw to cause it Vto slide along the helixes of resistance wire. At

its left-hand end the screw proj ectsbeyond the rear of the sleeve 14, and its ends are at- :attached to suitable lugs or projections on the housing, and is provided with a knurled head A 17 by which it may be manually rotated. Each resistance device has, end, a terminal connected with one'of two binding-posts 18 mounted on the housing.

A feature of the invention resides in the provision of certain adjustable stops to limit.

the movements of the contact-member. For this purpose the cover 8 is longitudinally slotted at the middle, and the arm 15 projects forwardly into the slot, which it traverses in one direction or the other when the adjusting screw is turned. The stops 19 and 20 are. in

^ the form of screws seated in the slot and cooperating with nuts 27 lying against the inner surface of the cover. When loosened, these screws may be moved along the slot and they may then be iixed at any desired point by tightening them. The stops cooperatewith the arm 15` to 'arrest movement of the sleeve 14, and the contact member, at anydesired point.

The controller is shown diagrammatiat its right-hand lto be energized by either direct current or alternating current of any -ordinary frequency. In sucha motor I have Jfound it deranged t sirable to use a certain amount of shunt winding, and to connect in series with such winding a` certain minimum amount of external resistance, together with a certain further amount of resistance which is variable to vary the speed of the motor. The amount of xed resistance and the amount of variable resistance depend upon the range of speed through which it is desired to control the motor, and upon the characteristics of the current by which the motor is to be energized,

and adjustment of these two factors may be conveniently made by moving the two stops 19 and 20 along the slot in the manner previously described. Since, however, there must at all times be a certain amount of ex-v ternal resistance in order to give the motor, to a .certain extent, the characteristic of a compound wound machine, and thus to prevent it from attaining excessive speed if accidentallyl unloaded, the controller is so arat, even in the Iextreme positionor` 20, it is impossible to move the conthe stop tact-member 12 ar enough'to cut out .all ofv the resistance. That is to say, even 1f the stop 20 be moved to the right-hand end of the slot, and the contact-member be moved as ar to the right as the stop will then permit, there is still, as shown in Fig. 2, a substantial length o the resistance devices extending to the right of the contact member and still included in the field circuit.

A. `motor of the kind in question is shown diagrammatica-lly at 21 in Fig. 1, this motor having a series winding 28 and a shunt winding 22. One terminal of the shunt winding is connected to one of the brushes 23, with the upper binding-post 18, while the lower binding-post is connected, by a wire 24, with the other brush of the motor. Ac-

which is particularly adaptedof the mo# tor, and the other end is connected,by a wire' through the latter to the other binding-post and back to the motor.

It will be noted that, since any movement of the contact-member cuts in or out equal amounts of resistance on both resistance devices simultaneously, the rheos'tat may be adj usted rapidly from one extreme to the other,

even though having a considerable length of wire, so that the motor speed may be controlled from one extreme to the other by a few turns of the knurled head 17.

Vhile the controller and the particular motor in question may be used for various purposes, they are' especially designed and adapted for use in power-operated machines such as typewriters, and they are shown diagrammatically as embodied in such a machine, the controller being xed, at the rear, upon a vertical plate or web 25 constituting a part of the frame 26 of the machine. When so used, the head 17 projects at the side of the frame, where it may be conveniently reached by the operator.

The invention claimed is:

1. A rheostat comprising: two resistance devices provided with parallel series of contact points, a screw lyingbetween and parallel with the resistance devices, a housing enclosing the resistance devices and provided with a slot parallel with the screw, a nut member, of insulating material, threaded upon the screw and comprising a lateral projection which engages said* slot to prevent turning of the nut member about the screw, and a Contact blade centrally perforated to receive said ,projection and spanning the two series of contact points. t y

2. A rheostat, as set forth in claim 1, cornprising also astop adjustably fixed in said slot and cooperative with said projection.

RUSSELL G. THOMPSON 

